Improvements in diagnosis and treatment of olfactory disease will require first, a more comprehensive analysis of the anatomical status of the olfactory periphery (the 1 cm2 areas on the nasal septum and the lateral nasal wall immediately inferior to the cribriform plate) with respect to the preservation of the olfactory epithelium (OE) and, second, a means of determining whether the OE's inherent capacity to reconstitute itself remains intact. We propose three specific aims designed to address our shortcomings with respect to the pathological bases of peripheral olfactory dysfunction. Aim 1: We observe a better than expected preservation of OE in the olfactory area of autopsy specimens, but immature neurons are abnormally prominent. We will test the hypothesis that areas in which immature neurons predominate are disconnected from the OB by using immunohistochemical analysis and DiI/DiO tracing of axons. Aim 2: The intermingling of OE and RE in the olfactory area and the occurrence of quiescent, aneuronal OE indicate that dysfunction of olfactory stem cells and progenitor cells contributes to peripheral olfactory pathology. Guided by our studies of the molecular profile of stem and progenitor cells in mouse and rat OE, we will identify markers for identifying neurocompetent stem and progenitor cells in human OE. We will screen for and analyze the expression of the human homologues of genes that are relevant in mouse using RT-PCR, IHC and in situ hybridization on human olfactory tissue collected by biopsy. We also plan open-ended gene profiling studies. The resulting panel can be used to assay for the stems and progenitors in human olfactory tissue. Aim 3: To test the usefulness of the stem/progenitor marker panel and the analysis of axon trajectory for the diagnosis of dysosmic patients. Guided by our studies of the olfactory area in Aim 1 we will harvest biopsies of the olfactory area from patients rendered dysosmic as a consequence of aging, chronic rhinosinusitis, or prior viral URI, and use our panel to analyze the status of stem and progenitor cells as well as the pattern of axonal growth within the tissue.